This work undertakes a comprehensive analysis of the US state experience under formulary apportionment of corporate income. While formulary apportionment eliminates the possibility of shifting income across states through accounting strategies that manipulate where income is booked, it may heighten the tax responsiveness of formula factors. The present analysis uses the substantial variation in corporate tax policy decisions of US states over the period 1986 to 2012 to understand the consequences of formulary apportionment better. It examines the effects of policy choices regarding tax rates, formula weights, and other parameters on economic activity, estimating the tax sensitivity of employment, investment, and sales. With the inclusion of adequate control variables, results indicate that economic activity has not been particularly sensitive to US state corporate tax policy choices, especially in recent years. Still, tax policy choices have important effects on corporate tax revenues. These results suggest important lessons regarding possible international adoption of formulary apportionment.